In the field of ion beam systems, it is sometimes desired to generate purified ion beams in the form of ribbon-shaped beams. These ribbon beams are commonly used in ion implanter apparatus and implantation systems where a workpiece (such as a silicon wafer or flat panel display) is moved through the ion beam. In these instances, the ribbon ion beam will desirably have a high aspect-ratio such that the beam is wider than any size-dimension of the workpiece undergoing implantation; so, that in a single pass through the ion beam, a uniform dose of ions may be implanted onto a surface and into the internal substance of the workpiece. In the performance of these applications, it is also very desirable that the ribbon beam has its ion trajectories moving in parallel and be carefully controlled to present a uniform current density profile suitable for the uniform implantation of ions into silicon wafers or flat glass panels.